Humans possess a remarkable ability to monitor their own mental processes, a property termed metacognition??. The proposed research investigates the neural mechanisms that underlie this capacity. Metacognitive judgments are important in everyday life and educational settings, where they play an important role in helping us to evaluate our own decisions?1,2?. Moreover, metacognition is impaired in a number of clinical conditions?3-5?. The proposed research is therefore likely to yield important clinical insights. The proposed research will address two fundamental questions about the neural mechanisms underlying metacognition. The first question concerns whether metacognition in the perceptual and memory domains is supported by the same mechanisms, or by ?domain-specific mechanisms??. Recent work has suggested that domain-specific mechanisms may exist in both the ?anterior prefrontal cortex (aPFC)??13,14,17? and the precuneus??13,14,16?. The proposed research will provide a causal test of these hypotheses by bidirectionally manipulating the content of specific representations in these regions. The second question concerns the distinction between ?metacognitive bias?? -- one?s overall level of confidence -- and ?metacognitive accuracy?? -- the extent to which decision confidence is predictive of decision accuracy?23?. A number of experiments have investigated the brain basis of metacognitive bias, but the brain basis of metacognitive accuracy is less well understood. Recent proposals have hypothesized that the ?aPFC plays an important role in metacognitive accuracy by integrating multiple sources of information that may inform a confidence judgment?15,24?. The proposed research will test this hypothesis by bidirectionally manipulating the content of specific representations in the aPFC. To accomplish the proposed research goals, we will use real-time fMRI Decoded Neurofeedback (DecNef)?15?. DecNef allows the content of specific neural representations to be manipulated, even allowing different representations within the same brain region to be controlled separately. Because many of the representations of interest overlap within the same region, DecNef is the perfect tool for manipulating these representations in a precise manner, and provides numerous advantages over other approaches. We plan to capitalize on these advantages to answer fundamental questions about the brain basis of metacognition which could not be addressed using previously available approaches. The sponsor?s laboratory is one of a few research groups with extensive expertise in DecNef?12,20,22?, and will be an excellent environment for training in this technique. Training in DecNef will add an important tool to the applicant?s previous training in fMRI, brain stimulation techniques, and computational modeling, and will prepare the applicant to transition to their next stage as an independent researcher.